1. Field of the Invention
The present invention relates to a motor generator, particularly to a motor generator without permanent magnet but with disc type axial air-gap structure.
2. Description of the Prior Art
Generally speaking, in order to obtain the motor generator with high power intensity and high torque intensity, the permanent magnet is used as the rotor magnetic force source for the technology. And in order to improve the power intensity and torque intensity, it is necessary to use strong magnet as the permanent magnet, in order to obtain stronger magnetic force. The rare earth metals are used as raw materials to make strong magnet. However, because the rare earth raw materials are exhausted day by day in recent years, therefore their price is higher and higher, which has exceeded the cost burdened by general motor gradually. Thus, the technical development of the motor generator transfers to magnet free motor generator instead of permanent magnet as the magnetic force source in recent years, such as variable reluctance motor, induction motor etc. However, the power intensity and torque intensity of this kind of magnet free motor generator are relatively low, which will be unfavorable to the application field of directly driven.
When the strong magnet is adopted as the magnetic force source for the rotor of motor generator, although the power intensity and torque intensity can be increased, yet the magnetic effect of permanent magnet will be lost because the temperature rises, which will cause the reduction of motor efficiency for a long period. In addition, the magnetic conductive rate of permanent magnet is extremely low, thus the thicker magnet will have larger magnetic resistance. Therefore, the permanent magnet design is hard to be adopted for several hundred kW industrial motor generator.
Therefore, it is necessary to design a direct driven motor generator without permanent magnet and reducer, to provide large torque output, and improve the drawback of variable reluctance structure.